1. Field of the Invention
The present invention relates to a heart rate counting device, and more specifically to a pulse rate counting device which obtains a pulse rate with high accuracy from unstable pulse wave data acquired during physical activity etc.
2. Description of the Related Art
Conventionally, a device for obtaining a pulse rate using a pulse wave sensor attached to the ear or finger of a user has become commercially practical as heart rate counting technology requiring smaller load for the user than electrocardiograph.
Pulse wave data is stable when the quantity of motion is small during walking etc. (refer to FIG. 1A), and can be used for detecting a pulse wave interval with high accuracy. However, the pulse wave data becomes unstable when the quantity of motion is large during running etc. (refer to FIG. 1B), and it is difficult to detect a pulse wave interval with high accuracy.
Therefore, in the conventional technology, a pulse rate is obtained using two sensors, that is, a pulse wave sensor and a physical activity sensor for detecting the physical activities as a physical activity signal using an acceleration sensor (for example, refer to the patent document 1) to solve the problem of unstable pulse waves caused by a large change in the pulse rate during physical activity.
However, in the conventional system, the physical activity sensor is required in addition to the pulse wave sensor, thereby causing the problem of increasing the load for a user in price and attaching operation.
Since there is less unstable pulse waves during resting or during moderate physical activity, the change in heart rate can be roughly classified into three levels, that is, a stable status, an increasing tendency, and a decreasing tendency, and the subsequent heart rate can be predicted depending on the current tendency.
During fast walking or running effective as aerobic exercise, there occurs more unstable pulse wave due to the physical activities, the displacement of a sensor, etc. Therefore, there occur various fluctuations such as repetitions of small changes in the waveform intervals in pulse waves, repetitions of increase and decrease in amplitude, etc., thereby causing the problem that it is difficult to detect a correct pulse only by determining an increasing tendency or decreasing tendency acquired from a simple average value of a previous measurement result.    [Patent Document 1] Japanese Published Patent Application No. H9-154825